The invention discloses a method for preparing asymmetric polymer nanospheres, and relates to polymer nanospheres. The method comprises the following steps: adding a hydrophile monomer, a hydrophobic monomer and saturated hydrocarbon into a solvent, introducing nitrogen, heating to implement polymerization reaction, further adding an initiator solution, and continuously introducing nitrogen to react, thereby obtaining the single dispersed asymmetric polymer nanospheres. As the asymmetric polymer nanospheres are prepared by using a soap-free emulsion one-step synthesis method, the method has the advantages that the operation is simple and feasible and the particle sizes of the obtained product, that is, irregular micro spheres, are uniform and controllable. As no emulsifier or stabilizer is added, the obtained product is pure, and polymer photonic crystal which is prepared later can be used without any treatment. The obtained product has the advantages of simple aftertreatment and high pioneering property, and has certain application prospect in medicinal fields such as medicine release and medicine carriers.